Humidifiers of various types are known. Some, which may be termed evaporative humidifiers, depend largely or entirely on relative movement between the air to be humidified and a water bearing surface. These include, for example, units wherein water is thrown from a high speed rotating wheel and rapidly enters the surrounding atmosphere as finely divided droplets, or wherein a moving airstream is directed past or through moving water bearing screens or porous members. Disadvantages of this general type of humidifier include the undesirable distribution of water droplets into the air, as well as mineral dust, bacteria and other contaminants from the water supply. Also, frequent cleaning maintenance is normally required, not only as to the evaporation unit itself but also as to environmental surfaces contacted by the thus humidified air.
Humidifiers of another type humidify by heating water sufficiently to generate steam, which is admitted to the atmosphere as the humidifying agent. Desirably, minerals in the supply water are not admitted to the humidified air, but rather remain in the heated water reservoir. Moreover, the boiling of the supply water to produce steam substantially kills bacteria and the like present in the water reservoir. Thus, a clean, sterile vapor is distributed to the environment.
It is known to generate steam by immersing electrodes in a supply of water present in an evaporating tank so that electrical current flows through the water between the electrodes and heats same to generate steam. The current amperage, and thus the amount of steam generated, depends on the electrical conductivity of the water and on the depth to which the electrodes are immersing in the water. In order to control the amount of steam that is generated, some of the water in the evaporating tank is drained to prevent buildup of the mineral salt content thereof, thereby to control the electrical conductivity of the water, and also the water level in the tank is controlled, thereby to control the current amperage. The electrical conductivity of tap water varies widely depending on the source thereof, e.g., city water mains, wells, etc. This introduces vexing problems of maintaining properly controlled water conductivity. Careful adjustments of electrical control circuitry are needed and individual adjustments are usually required at each installation.